Imperfect combustion of hydrocarbon fuel for automobiles causes carbon materials to be formed or deposited on many sites within the engine of automobiles. These carbon deposits within the engine combustion chamber have a deleterious influence on the engine. For example, the carbon deposits within the combustion chamber reduce its space, so that, when a fuel-air mixture is compressed, a compression ratio higher than a designed one is obtained, causing a knocking phenomenon. Protracted engine-knocking gives stress fatigue or abrasion to main parts of the engine, resulting in increasing the maintenance cost of automobiles and reducing its life span.
Also, it is known that, when idling or driving an automobile at low speeds, the carbon deposits formed within its engine interrupt the flow of air so that a overfull-air mixture is injected into the engine. The mixture is imperfectly burned, to make the engine idle roughly and to exhaust excess hydrocarbons and carbon monoxide.
U.S. Pat. No. 4,881,945 discloses that alkylphenyl poly(oxyalkylene)amino carbamate is effective for controlling the amount of fuel deposits. According to this patent, alkylphenyl poly(oxyalkylene)alcohol is reacted to phosgene to synthesize an intermediate of chloroformate which is, then, reacted to polyamine, to give a desired alkylphenylpoly(oxyakylene) aminocarbamate. However, extreme care must be taken of phosgene gas because it is highly toxic. Further, the phosgene gas left unreacted in the reaction and the hydrochloride gas produced during the reaction must be removed, which makes the production process more complicated.
According to many patents including the above-cited patent and U.S. Pat Nos. 4,160,648, 4,243,798, 4,191,537 and 4,197,409, polyamine is used at 15-fold equivalents relative to chloroformate, the intermediate, to produce a desirable monoaminocarbamates, which are used as an additive for controlling fuel deposits. The excess polyamine used must be removed by washing with distilled water after the reaction. This is economically unfavorable because polyamine is unnecessarily consumed or a further process is required to reclaim the excess polyamine in addition to the washing process.
When polyamine is reacted with chloroformate, polyamine hydrochloride is produced at the same moles with aminocarbamates, the desired product. The chloride salt thus produced is unfavorable to the fuel oil and may be a cause of corrosion and plugging up the engine. Accordingly, the problematic compound must be reduced into a very low level or completely removed.
U.S. Pat. No. 5,468,263 to Chung et al., which is assigned to Yukong Limited, discloses that an alkylphenyl poly(oxyalkylene)polyamine acid ester compound as a fuel detergent is prepared by reacting alkylphenyl poly(oxyalkylene)maleate derivate compound with polyamine at an equivalent ratio of 0.5:1 to 1:20. The excess polyamine used must be removed and this is economically unfavorable because polyamine is unnecessarily consumed or a further process is required to reclaim the excess polyamine. Furthermore, the polyamine left unreacted in the reaction affects adversely the storage stability of the final products, for example, when storing in an oven maintained at 54.degree. C. for one month, a deposit is generated in an average amount of 0.1 to 0.2 wt % and the detergent becomes turbid.